1. Field of the Invention
This invention relates to traction drive fluids, more particularly to a traction drive fluid used not only for a power transmission mechanism such as the automatic transmission of traction drive type for an automobile but also for the hydraulic control mechanism thereof as well as the friction characteristics controlling mechanism for the wet clutch.
2. Prior Art
In the industrial machinery field, traction drive fluids have already been used for traction drive type power transmission devices which are designed to transmit power via a film of oil formed at the contacting surfaces of the operative parts. Such traction drive fluids used in these devices are required to have high traction coefficient, i. e. superior power transmission capabilities.
In recent years, extensive studies and investigations on a traction drive fluid have been made for its use of the continuously variable transmission of an automobile. When used for an automobile, the fluid is used not only for the power transmitting mechanism but also for the hydraulic controlling mechanism as well as the friction characteristics controlling mechanism for the wet clutch.
There has been known an automatic transmission fluid (ATF) which is a lubricant used for the hydraulic controlling mechanism and the friction characteristics controlling mechanism for the wet clutch constituting the transmission of an automobile. It is a well-known fact that ATF is required to be higher than a certain level in a kinematic viscosity at elevated temperatures and superior in flowability at low temperatures for performing the role of the hydraulic controlling mechanism. It is also well known that ATF is required to be blended with additives which are excelled in friction characteristics, particularly in shudder resistance characteristics for fulfilling the requirements in performing the role of the friction characteristics controlling mechanism, particularly the controlling mechanism having in addition slip controlling capabilities.
In the case where a traction drive fluid is used for the continuously variable transmission of traction drive type for an automobile, it is necessary for the fluid to have not only inherent superior power transmitting capabilities but also the capabilities required for ATF, that is, capabilities upon being used as a fluid for the hydraulic controlling mechanism and the friction controlling mechanism of the wet clutch.
Although there is a commercially available traction drive fluid sold under the tradename of "SANTOTRAC" which is widely known to have an excellent power transmitting capability, a traction drive fluid suitable for an automobile has not been place on the market because it needs to fulfill the requirements on the capabilities such as a flowability at low temperatures which are expected to exhibit upon being used for the continuously variable transmission of an automobile.
In view of the current situations, an object of the present invention is to provide a traction drive fluid which is excellent in not only power transmitting capabilities but also the capabilities required as a fluid for controlling hydraulic pressure and the friction characteristics of a wet clutch constituting the transmission of an automobile.